Short pulses are understood to be pulses whose duration may range from 1 to 1000 picoseconds. When the pulse to be analyzed is a short but repetitive pulse, normally a sampling of this pulse is taken by means of using a sampling oscilloscope which samples part of the information from each pulse and thus, via this part, constructs the form of the pulse. This sampling technique may only be applied to repetitive pulses.
In the case of short but non-repetitive pulses, a slit scanning camera is traditionally used in which display of the phenomenon onto a storage tube linked to an electronic deflection has a temporal revolution close to a picosecond for photonic pulses (X-rays, infrared or visible ultraviolet rays). However, the use of such a slit scanning camera cannot be easily implemented in certain usages owing to the large geometrical dimensions of the camera. Moreover, this camera is costly and secondly it is difficult to exploit the image supplied as the latter needs to be retaken by another camera.
The method is also known for using an electro-optical autocorrelating device in order to measure a nonrepetitive short pulse or a repetitive but coherent pulse. Such autocorrelators use non-linear crystals which make it possible to reach the sub-picosecond field. However, such autocorrelators may only be used for coherent light pulses.
Furthermore, a multichannel autocorrelator exists which is embodied from photoconductors connected to lines for the propagation of electric signals generated by the photoconductors. Such an autocorrelator was exhibited at San Diego in August 1987. However, such a correlator does not make it possible to give the form of a pulse in a single shot, in other words from a single pulse in the case where the pulse is an electric pulse. Moreover, in the case of electromagnetic pulses, this device may only be used for a predetermined range of pulse durations, the limited number of points of the autocorrelation function being linked to a pulse whose average duration is known. Furthermore, this aforementioned device comprises as many delay lines as many as the measuring points of the autocorrelation function. The various photoconductors associated with each delay line only allow for temporal measurements very close to each other to be made and only make it possible to know the inclination of the incident beam with respect to its axis of propagation. This axis is assumed to be perpendicular to the plane of the detector photoconductors. The various delay lines have different lengths so as to obtain various points of the autocorrelation function of a pulse.
Via the U.S. Pat. No. 4,482,863, a device is known which measures the transfer function of a circuit, this device comprising a single delay line along which and disposed several photoconductive elements. These elements are spaced at regular intervals on the delay line so as to introduce equal times for propagating the electric wave circulating on this line between the various photoconductors. Various points of the temporal form of an electric pulse are thus obtained.
In the device described in this patent, the photoconductive elements and the lines for propagating the electric signals are surface-technology (substrate strip). This presents action significantly limits the useable polarization voltages, failing which ionization of the air between the electrodes close to the photoconductive elements introduces a parasitic current capable of introducing ill-timed breakdowns. This limitation introduces a significant loss of sensitivity which explains the need function with repetitive pulses. Thus, this device makes it possible to carry out by sampling an analysis of the electric pulse by optically introducing the delay required for the sampling function.
Moreover, it is necessary that optics be associated with the device so as to delay the entry of the optical pulse required in order to analyze each photoconductor.
As a result, no device of the prior art makes it possible to obtain either the temporal analysis or autocorrelation function of a short electromagnetic radiation or ionizing pulse in a single go, or the temporal form of an electric pulse.